Since optical discs such as Compact Disc Digital Audio (CD-DA) discs and Compact Disc Read Only Memory (CD-ROM) discs are easy to handle and their production cost is relatively low, they have been widely used as recording mediums that store data. Moreover, in recent years, Compact Disc Recordable (CD-R) discs that allow data to be written once and Compact Disc Rewritable (CD-RW) discs that allow data to be rerecorded have come out. Data can be easily recorded on such discs. Thus, optical discs based on the CD standard such as CD-DA discs, CD-ROM discs, CD-R discs, and CD-RW discs have become the mainstream of data recording mediums. Furthermore, in recent years, technologies for compressing audio data in accordance with the MPEG1 Audio Layer-3 (MP3) system and the Adaptive Transform Acoustic Coding (ATRAC) system and recording the compressed data on a CD-ROM disc, a CD-R disc, a CD-RW disc, or the like has been used.
However, as CD-R discs and CD-RW discs have come out, data recorded on a CD can be easily copied to such discs. Thus, there is a problem about copyright protection. As a result, when content data is recorded on a disc such as a CD disc, it is necessary to take countermeasures for protecting content data against copyright infringers.
FIG. 15 schematically shows a process of a copy operation. A reproducing unit designated by reference numeral 41 reproduces content data from an original disc for example a CD 42. Reference numeral 43 represents an optical pickup. Reference numeral 44 represents a reproduction signal process portion. Reproduction data reproduced by the reproducing unit 41 is supplied to a recording process portion 52 of a recording unit 51. An optical pickup 53 records the reproduction data to an optical disc for example a CD-R 54. The content data recorded on the CD 42 is recorded to the CD-R 54. In such a manner, with the reproducing unit 41 and the recording unit 51, a copy disc of the CD 42, which is an original disc, can be easily produced.
When a CD is used, as shown in FIG. 16, in the reproducing process portion 44, a sync detecting portion 46 detects a frame sync from a reproduction signal received from an input terminal 45. An EFM demodulator 47 demodulates the reproduction signal in accordance with the Eight to Fourteen Modulation (EFM) system and supplies the EFM-demodulated reproduction data to a Cross Interleave Reed-Solomon Code (CIRC) decoder 48. The CIRC decoder 48 corrects errors of the EFM-demodulated reproduction data. In the EFM system, each symbol (eight data bits) is converted into 14 channel bits. Three merging bits are added between two sequences of 14 channels bits. A sub code decoder 49 decodes a sub code from the reproduction data and obtains a reproduction sub code.
FIG. 17 shows an outlined structure of the recording process portion 52. Data to be recorded is supplied from an input terminal 55 to a CIRC encoder 56. The CIRC encoder 56 encodes the data in accordance with the CIRC system. In addition, a sub code is supplied from an input terminal 57 to a sub code encoder 58. The sub code encoder 58 converts the sub code in a sub code format. An output of the CIRC encoder 56 and an output of the sub code encoder 58 are supplied to a multiplexer 60. In addition, a frame sync is supplied from an input terminal 59 to the multiplexer 60. The multiplexer 60 arranges the input data of the three types in a predetermined sequence. An output of the multiplexer 60 is supplied to an EFM modulator 61. The EFM modulator 61 performs an EFM modulating process for the multiplexed data.
As one method for protecting content data recorded on a CD disc, it is determined whether or not a disc is an original disc or a copy disc on which data of an original disc has been copied. When a disc is an original disc, its content data can be permitted to be copied to another disc. In contrast, when a disc is a copy disc, its content data can be prohibited form being further copied to another disc.
To determine whether a disc is an original disc or a copy disc, a method for inserting a defect into a master disc upon production thereof, detecting the defect from a disc upon reproduction of an original disc, and determines whether the disc is an original disc or a copy disc with the defect has been proposed. However, in this method, such a defect is contained in an original disc. In addition, depending on the type of a defect that is contained in a disc, the defect may be directly copied to a CD-R disc.
The applicant of the present invention has filed a patent application of an invention about a data recording medium, a data recording method, and an apparatus that allow a disc to be determined whether it is an original disc or a copy disc without need to intentionally insert a defect in the original disc so as to prevent content data of an original disc from being copied (as Japanese Patent Application No. 2002-105278).
According to the invention of the prior patent application, a copy protection is performed using Digital Sum Variation (DSV). In other words, by recording predetermined data to an original disc, although its content data can be normally reproduced, since the predetermine data causes the DSV to deviate, content data cannot be normally reproduced from a copy disc such as a CD-R disc to which the content data has been copied from the original data.
When data is recorded on a disc, a plurality of symbols, for example, 24 symbols are encoded with an error correction code. A plurality of parities, for example, four parities are added to the data. Likewise, the predetermined data that causes the DSV to deviate is encoded with an error correction code and the parities are added thereto. The data to which the parities have been added causes the DSV to deviate.
In a conventional error correction code encoder, the phases of 24 symbol to be encoded are not specially designated. When the 24 symbols of the predetermined data having a particular phase (offset is 0) are encoded with an error correction code, the encoded data causes the DSV to deviate. However, when the phase of the predetermined data deviates and the offset thereof is not 0, the generated parities may be different from those generated when the offset is 0. As a result, the data that has been encoded with the error correction code may not cause the DSV to deviate.